63 lines
1.6 KiB
Go
63 lines
1.6 KiB
Go
package lockfile
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import (
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"fmt"
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"os"
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"path/filepath"
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"time"
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)
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const (
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lockFileName = ".ekdns.lock"
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staleTimeout = 2 * time.Minute
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retryInterval = 200 * time.Millisecond
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maxWait = 2 * time.Second
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)
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// Lock represents an acquired lock file that can be released.
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type Lock interface {
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Release() error
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}
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type fileLock struct {
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path string
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}
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// Release deletes the lock file. It is safe to call more than once.
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func (l *fileLock) Release() error {
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err := os.Remove(l.path)
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if err != nil && os.IsNotExist(err) {
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return nil
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}
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return err
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}
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// Acquire creates a lock file in dir and returns a Lock that can release it.
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// It waits up to maxWait for a stale or otherwise held lock to clear.
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func Acquire(dir string) (Lock, error) {
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lockPath := filepath.Join(dir, lockFileName)
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deadline := time.Now().Add(maxWait)
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for {
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f, err := os.OpenFile(lockPath, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0644)
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if err == nil {
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// Write PID for debugging (not used for staleness detection)
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fmt.Fprintf(f, "%d\n", os.Getpid())
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f.Close()
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return &fileLock{path: lockPath}, nil
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}
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if !os.IsExist(err) {
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return nil, fmt.Errorf("creating lock file %s: %w", lockPath, err)
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}
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// Lock file exists — check staleness
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info, statErr := os.Stat(lockPath)
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if statErr == nil && time.Since(info.ModTime()) > staleTimeout {
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os.Remove(lockPath)
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continue // Retry after breaking stale lock
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}
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if time.Now().After(deadline) {
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return nil, fmt.Errorf("could not acquire lock file %s: another instance may be running", lockPath)
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}
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time.Sleep(retryInterval)
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}
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}
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